Damage to building structures and plants caused by insects represents a formidable problem affecting a wide variety of construction and agricultural activities. Considerable effort is devoted by manufacturers of insecticides to develop safe and effective products for controlling such pests as ants, roaches, termites, and many others. An area of growing concern among manufacturers and regulators has been the impact that insecticides can have on the environment. In conventional methods for applying insecticides to control insects, the insecticide is typically applied in liquid, powder or granular form to the area in which it is desired to control insects. When the insecticide is applied onto soil or into an area of a building structure, there is a substantial likelihood that the insecticide, through the action of water or other mechanisms, will migrate from the area of application to other areas in which it is undesired. For instance, runoff of insecticides into waterways represents a serious environmental problem.
Additionally, insecticides applied in the conventional manner are subject to being degraded by dilution caused by water and by the action of microorganisms in the soil to which the insecticide is applied. The migration and degradation result in failure to provide long-term control. As a result, it typically is necessary to periodically re-apply insecticide to the area to be protected. Unfortunately, such re-application only exacerbates the environmental problems noted above.
For the above reasons, increasing attention is being paid to the development of controlled delivery devices for making insecticides available where they are needed while preventing the uncontrolled release or migration of the insecticide to undesired areas. U.S. Pat. No. 5,801,194 discloses a termite and boring insect ground barrier for protecting wooden structures, comprising a controlled release device formed as a sheet of spun-bonded polymer material having stripes or spots of a mixture of polymer and insecticide bonded thereto. The stripes are about one centimeter in height and spaced apart about 5 to 15 centimeters. The spots are about 0.5 to 1.5 centimeters in both diameter and height and are spaced apart about 1.5 to 4 centimeters. The '194 patent also discloses a foam sheet having pellets of the polymer and insecticide mixture embedded therein. The insecticide is present in the polymer in a concentration of about 5 to 30 percent by weight. The patent teaches placing the controlled release devices in various positions near a wooden structure to purportedly provide a means for a slow and relatively constant release of insecticide in order to create a barrier zone for insects in the soil around the structure. The controlled release devices are relatively complicated in their construction, which would likely render the devices prohibitively expensive to use in most building construction applications.
U.S. Pat. No. 2,899,771 discloses a two-layer insect resistant vapor barrier comprising a polyethylene film coated with a water soluble carrier impregnated with an insecticide. The '771 patent teaches placing the vapor barrier between a slab and the soil on which the slab is supported. Condensation forming on the vapor barrier is said to cause the insecticide to be released into the soil to act as a soil poison. With such a device, repellancy of insects is likely to be effective for only a relatively short period of time, as the carrier fully dissolves and releases all of the insecticide into the soil where it can be dispersed and/or broken down by the action of water and/or microorganisms in the soil.
U.S. Pat. No. 5,860,266 issued to Martinet et al. discloses a method for protection of buildings against termites, in which a non-porous film of plastic material impregnated throughout with a low concentration of an insecticide is laid over the entire erection surface of the soil prior to erection of the foundation and structure. Where intentional holes are made in the film, such as for the passage of pipes or conduits into the building, the soil near the holes is laced with pellets of plastic material impregnated with insecticide. The pellets are also applied to the soil in regions where unintentional or accidental tears or rips of the film may be likely, such as around the bottoms of foundation footers. The method relies on creating a plastic film barrier over the entire surface of the building foundation such that the barrier is between the foundation and the adjacent soil. A drawback of Martinet's method is that application of plastic film over the entire erection surface is not a standard building practice, and thus there may be some resistance to its adoption by construction contractors. Furthermore, the method is amenable only to new construction. Martinet does not teach any method for treating existing structures.
In some cases, certain standard or common construction practices can actually make it more difficult to protect a structure against termite infestation or to treat a structure that is already infested. For instance, a construction practice developed in Canada for energy-efficiency purposes comprises wrapping the foundation in thermally insulating foam board. This concept was adopted by the U.S. Department of Energy and was included in the federal Model Energy Code, which recommended installing foam insulation around slab foundations as much as four feet below ground. Accordingly, many builders in the late 1980s and early 1990s followed the Model Energy Code. Unfortunately, at about the same time, two insecticides that previously had been widely used for the control of termite infestation—chlordane and heptachlor—were banned by the U.S. Environmental Protection Agency. The insecticides that are now used instead have significantly less staying power in the soil and are less potent. It has since been found that many of the structures built with foam insulation near or below ground are subject to significant termite infestation problems, because the termites tunnel through and/or behind the insulation and are nearly impossible to eradicate. Spraying the foam insulation with insecticide does not work because the foam is waterproof.
In an effort to solve such problems, Clemson University researchers tried lacing foam board with boric acid, which kills termites if they ingest it. However, the researchers found that the boric acid did not prevent termites from building mud tunnels between the foam and the foundation. Thus, this apparent solution turned out to be a failure. In view of the problems associated with foam insulation, there are efforts in some states to prohibit the use of foam board in proximity to soil. It would be desirable, however, to be able to use foam insulation near soil because of the beneficial thermal insulative properties it possesses.
The agricultural industry is also significantly impacted by the damaged caused by insects. In the citrus industry, it is common practice to graft one variety of citrus plant into a hardy root stock of another variety. The root stock is selected, for example, to be drought-resistant, disease-resistant, etc., so that the citrus tree will survive and thrive from season to season and year to year. The fruit produced by the root stock, however, is undesirable, so a more-desirable variety is grafted into the root stock. The root stock typically extends about 12 inches or so above the soil line. Conventionally, citrus growers have wrapped the root stock with a thick plastic film or a polystyrene sleeve from the soil line up to about 18-24 inches above the soil line. This is done for one critical reason: The wrap prevents the root stock from putting out limbs that would produce unwanted fruit. However, in recent years, the practice of wrapping or sleeving root stock has been halted in some areas because certain insects, notably ants (including imported fire ants) and termites, take up nesting in the wraps or sleeves and tend to damage the plant stem, leaving the plant susceptible to disease if not killing the plant immediately. Attempts have been made to overcome this problem by placing a slow-release insecticide device between the plant stem and the wrap or sleeve. The slow-release device is a bag holding a quantity of insecticide and designed to slowly release insecticide from the bag. However, this solution is too costly to be practical. Thus, a more cost-effective solution to this problem is needed.
Furthermore, in the growing of many types of crops such as strawberries, tomatoes, eggplants, cucumbers, melons, squash, peppers, and others, it has been common practice to cover the soil with plastic film, also known as plastic mulch, for various purposes. The plastic mulch can be used to absorb solar energy and warm the soil in cooler climates so as to enable earlier crop production (or, alternatively, to reflect heat from the soil in warmer climates). The plastic mulch also improves moisture retention so that less irrigation is needed, inhibits growth of weeds, reduces leaching of fertilizer, and prevents contact of growing produce with soil and thus prevents rot and other soil contact-related damage. Another function of plastic mulch is to help insure that insecticidal fumigate injected into soil to control disease and insects remains in the soil, and to minimize release of toxic gases from the fumigate into the air. Methyl bromide is currently the fumigant used for this purpose, but EPA regulations promulgated to carry out the objectives of the U.S. Clean Air Act call for a gradual phaseout of methyl bromide over the next few years, with a complete ban becoming effective in 2005. Thus, an effective alternative to methyl bromide for growing crops is needed.
Yet another problem in the agriculture industry is unintentionally shipping insects with freshly harvested produce from grower to distributor to retailer. The case of the Mediterranean fruit fly is a classic example. Interstate and international shipments of produce can be subject to quarantine and rejection or destruction if the shipments are infested with particular pests. To avoid such a result, many shippers treat produce with low levels of pesticides to kill any insects on the produce prior to shipment. It would be desirable to have an alternative solution not involving the application of pesticides to the produce.